Ostracods' diet

Most free-living ostracods are considered to feed on algae and organic detritus, but some ostracods are omnivores, predators and scavengers. Additionally, some ostracods have commensal relationships with (mostly) other larger crustaceans, such as crayfish, while a small number of ostracods are parasites on sharks, sea urchins, polychaete worms and amphipods.

Whether ostracods are prey or predator of certain groups can be related to population densities. In experiments with fish fry and ostracods, it was noted that the fish eat the ostracods, but if the number of ostracods is large, the tables are tuned; the ostracods attack and eat the fish fry, leaving just the vertebrae and scales (Liperovskaya 1948).

In the marine genus Rutiderma males and females have different feeding strategies; females are predators, while males, with more poorly developed maxillae, are probably detritus feeders (Kornicker 1985).

Food

Notes

References

Organic detritus

Organic detritus (i.e. the remains of dead organisms and faecal material) is an important food source for many species.

A wide variety of algae is eaten by ostracods, including diatoms, single-celled algae, colonial algae and filamentous algae. In a study, a large quantity of algae was found in the guts of nine freshwater ostracod species. Marine myodocopids also consume algae (e.g. diatoms) as well as other things.

Studies have shown that a small part of the diet of the marine giant ostracod Gigantocypris muelleri is made up of other ostracods, and marine planktonic halocyprid ostracods are consumed by Macrocypridina castanea. In non-marine habitats, Australocypris insularis was reported to feed on other smaller ostracod species, while Heterocypris incongruens is known to be cannibalistic.

The remains of a mysid have been reported from the stomach of Macrocypridina castanea.

Cannon 1933

Krill (Crustacea, Euphausiacea)

Parts of krill appendages have been found in the stomachs of Macrocypridina castanea.

Kornicker et al. 1976

Water fleas (Crustacea, Caldocera)

As well as consuming dead cladocerans, ostracods also predate on live specimens. Observations revealed that ostracods attack the antennae of Daphnia first, immobilising the victim before killing and eating it.

Liperovskaya 1948; Fryer 1997

Non-biting midge larvae (Insecta, Diptera, Chironomidae)

Ostracods have been known to eat non-biting midge larvae by attacking in groups.

Rossi et al. 2011

Mosquito larvae (Insecta, Diptera, Culicidae)

Mosquito larvae can be attacked and eaten by ostracods.

Rossi et al. 2011

Snails (Mollusca, Gastropoda)

The young of freshwater snails are predated on by ostracods, including snails that are a vector of the disease schistosomiasis. A shell of a heteropod (planktonic gastropod) was recovered from the stomach of a marine ostracod.

Müller 1890; Sohn & Kornicker 1972

Amphibian eggs (Amphibia, Anura)

Some common species of freshwater ostracods have a taste for both toad and frog eggs.

Gray et al. 2011; Ottonello & Romano 2011

Fish (Osteichthyes)

Young fish have been found from the guts of the marine giant planktonic ostracod Gigantocypris mulleri, and freshwater fish fry can also be attacked by ostracods. The marine bioluminescent ostracod Vargula tsujii is reported to feed on the mucus and small pieces of skin of live fish, apparently not causing serious damage, but if the fish is attacked by isopods, Vargula tsujii will enter the fish's wounds to feed on the internal organs.

Cannon 1940; Liperovskaya 1948; Stepien & Brusca 1985

Dead animals

A variety of dead animals, such as fish, squid, annelid worms etc. are scavenged by some species of ostracods.

Vannier et al. 1998

Note that studies of gut contents of ostracods are not able to determine if organisms have been actively predated or scavenged.

Parasitic and commensal ostracods

Host

Notes

References

Sharks and rays (Chondrichthyes)

The myodocopid ostracod Sheina orri is a parasite on the gills of the epaulette shark and the bluespotted ribbontail ray, while Vargula parasitica has been found on the gills and in the nasal tubes of hammerhead sharks.

Wilson 1913; Bennett et al. 1997

Fish (Osteichthyes)

The marine bioluminescent ostracod Vargula tsujii is a noctunral feeder on the mucus and small pieces of skin of live fish, apparently not causing serious damage. Occasionally, fish will shake off the ostracods or swim away. If the fish is injured, the ostracods may predate the fish (see above table). A handful of Vargula parasitica specimens have been recovered from the gills of two species of fish, the rock hind and the blue runner.

Wilson 1913; Stepien & Brusca 1985

Decapods (Crustacea, Decapoda)

The Cytheroidea family Entocytheridae is a large groups of about 220 species, most of which are found clinging to crayfish in an apparent commensal relationship. They are also found on a species of freshwater crab.

Hart & Hart 1974

Amphipods (Crustacea, Amphipoda)

Several species of Paradoxostomatidae ostracods of the genus Acetabulastoma are parasites on amphipods. Some Entocytheridae species are commensal on amphipods.

Schornikov 1970; Hart & Hart 1974

Isopods (Crustacea, Isopoda)

Groundwater isopods are the hosts of a small number of Entocytheridae species.

Hart & Hart 1974

Sea urchins (Echinodermata, Echinoidea)

Sea urchins in the Pacific are the hosts of the genus Echinophilus, a parasitic genus of Paradoxostomatidae. A species of the Pontocypridoidea genus Pontocypria is also found in association with echinoids, although the exact relationship remains unclear.

Schornikov 1973; Maddocks 1979; Kretzler 1984

Starfish (Echinodermata, Asteroidea)

Pontocypria helenae can be found clinging to the tube feet of three species of Antarctic starfish, in a probable commensal relationship.

Maddocks 1968

Polychaete worms (Annelida, Polychaeta)

Mungava riseri, a marine Candonidae, is found attached to and eating the gills of a polychaete worm.

Maddocks 1979

Sponges (Porifera)

A study of a marine sponge collected in Madagascar, revealed a commensal species, Pontocypria humesi, living inside. In Lake Titicaca, Chlamydotheca incisa, normally found in temporary habitats, was found associated with a freshwater sponge.

Maddocks 1968; Martens & Harrison 1993.

The red swamp crayfish - a home for entocytherid ostracods.

Often the exact relationship between symbiotic ostracods and their hosts i.e. if they are parasitic or commensal, is not clearly known.

The entocytherid ostracods are mostly found on crayfish, and probably feed on detritus on the body of their hosts, but their ecology is poorly understood.

References

Arashkevich, E. G. 1977. A relationship between the daily feeding rhythm and the vertical migration of Cypridina sinuosa (Ostracoda, Crustacea) in the western part of the equatorial Pacific. Okeanologiya, 17, 707-712.